Method for coating the interior wall of hollow bodies



Aug. 4, 1931. A. M. HAGEMAN ET AL 3 30 METHOD FOR COATING THE INTERIOR WALL OF HOLLOW BODIES Original Filed Dec. 9, 1927 I FTQFA- INVENTORS AM. HAGEMAN BY A. F. Lwnsmom Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE AARON M. HAG-EMAN, OF BLOOMFIELD', AND ALBERT F. LINDSTROM', OF NUT'LEY, NEW

JERSEY, ASSIGNORS TO WESTINGHOUSE LAMP COMPANY, A CORPORATION 01! PENN- SYLVAN IA METHOD FOR COATING THE INTERIOR WALL OF HOLLOW BODIES Original application filed December 9, 1927, Serial No. 238,734. Divided and this application filed July 24, 1928. Serial No. 295,091.

This invention relates to the method of coating hollow bodies, particularly vitreous articles such as incandescent electric lamp bulbs or the like, and is a division of our applic ption Serial #238,734, filed December 9, 192

In the manufacture of incandescent electric lamps, it is important to' be able to provide a bulb which is made either of a light diffusing vitreous material or of a clear glassbulb having a coating of a light diffusing character and at the same time, obtain a maximum light efficiency. It has been proposed to obtain light diffusing effects by the employment of a so-called opalescent or opal glass, the opalescent effect being attained by adding cryolite to a batch of glass during manufacture. This was an expensive procedure and furthermore, such glass acts to decompose liberating gases, probably silicon-fluoride which are detrimental to the filament and shorten the life of the lamp. Furthermore, the light absorption by reason of opal glass is extremely high and inasmuch as it is not possible to obtain a uniform thickness of a bulb, the resultant transmitted light varied in intensity.

The nearest approach to the opalescent effect in connection with coated lamps was at tained by the application of a coating to the outer surface of the bulb such, for example, as that set forth in Patent 1,613,758, filed January 11, 1927.

The outside coating of bulbs, however, although giving a satisfactory light diffusing medium, did not attain the desired opalescent effect which may be defined as a light diffusing medium enclosed in a glossy or highly polished surface as the exterior surface of a lamp bulb.

It has beenproposed to etch the inside. surface of a lamp bulb with an acid such as a hydrofluoric acid or other etching solution. This method physically changes the inner surface of the bulb, breaking the same into numerous minute hills and valleys which reflect light at all anglesand cause a diffusion of the emitted light. The etched surface,

however, did not answer the requirement'of producing a; desirable opalescent effect, since the intensity of a lamp filament is too great to be diffused uniformly by the roughened surface of the bulb and although the transmitted light was difiused to an appreciable degree, a concentrated spot of light always with the smooth exterior surface of the bulb gives the desired opalescent or pearly effect. As set forth inour copending application Serial #737,609, filed September 13, 1924, for

coated article and method of making the.

same, the desired opalesoent effect is attained by applying a light diffusing material to the inside surface of a lamp bulb and it is an object of the present invention to provide a method whereby such material may be applied in a uniform and expeditious manner.

Another object of the invention is to provide a method of coating the inside surface of a hollow transparent body with a uniform light diffusing layer.

Another object of the invention is to produce a lamp bulb comprising a uniform light diffusing layer on the inside surface of a translucent body, which layer in combination with the glossy exterior surface of the, body will constitute a light diffusing medium, giving the desired opalescent effect.

The smooth outer surface of a lamp bulb or other container provided with a light diffusing inner layer is not only desirable from an ornamental standpoint, but provides an article in which the light diffusing lamp may have the required depth of color as when using various colored pigments.

The invention is, of course, applicable for the coating of various forms of hollow translucent bodies, but is herein shown and described in connection with the coating of the inner wall of a transparent vitreous incandescent electric lamp bulb.

The above mentioned type of hollow body, namely a lamp bulb, comprises a sphere-like portion terminating in a relatively narrow opening or neck. The application of a coating material to the inner surface of this form of hollow body is extremely difficult, particularlysince it is essential to apply the coating in suchmanner as to have the same uniform density throughout.

In an electric lamp bulb wherein a high temperature filament is disposed in close relation to the light diffusing wall, it will be appreciated that any variation or defect in the character of the coating will be exaggerated and readily noticeable, giving the bulb an unfinished or defective appearance.

In accordance with the present method, therefore, it has been found that by first heating a bulb to a given temperature and then applying a finely divided material to the inner surface of the bulb, preferably while the bulb is rotating, a layer of light diffusing material may be uniformly deposited. It

has further been found that the coating is best applied when discharged in the form of a spray such as a coniferous discharge from a spray gun nozzle. .The discharge is produced within the bulb and directed to a wall thereof, While a relative movement between the bulb and the spray nozzle is effected until the entire surface of the bulb receives a light diffusing layer.

The manipulation of the spray gun is important by reason of the close working relation necessary, inasmuch as the spraynozzle is confined to the space within the bulb. The

movement of the bulb and spray nozzle during the spraying operation, preferably a rotation of the bulb, results in the deposit of a layer of sprayed material.

As the nozzlemoves toward the end of the bulb, thecontour of the bulb is such that the distance between the spray nozzle and the bulb decreases. thus a rotation of the bulb causes the surface of the bulb at the narrow portion (or dead center of rotation) near the end to rotate at aless speed than the wider ortion. Normally, therefore, the end of the Bulb would receive an excessive amount of sprayed material. To avoid this, the spray deposited upon the other portions of the bulb in the direct path of movement of the spray discharge.

After the bulb has been sprayed, it may be moved into a baking oven to dehydrate the coating. This baking operation depends, of course, upon the character of coating employed.

The present method of coating by the apparatus employed results in a uniform deposit of coating upon the inner wall of a bulb and gives an article having a uniform light diffusing medium which, incombination with the lustrous outer surface of the bulb, provid es the desired op-alescent effect.

The invention will be more fully understood by reference to the accompanying drawings, in which Figure 1 shows a bulb in position to be sprayed and With the spray gun about to enter the bulb; i

Figure 2 is a view which shows the spray un within the bulb with a discharge of spray projected to the surface of the bulb;

Figure 3 shows a spray gun in its advanced position within the bulb to spray the upper portion thereof; and

Figure 4 shows a holder in which a bulb may be rotated during a sprayingoperation.

An apparatus for practicing the present method is more fully shown and described in the above mentioned copending application, of which this application is a division. In the said copending application, mechanism is shown comprising a conveyor having thereon a plurality of bulb holders for supporting lamp bulbs, the conveyor moving intermittently in stages so that the bulbs are applied to spraying mechanism. An oven is shown in the path of movement of the bulbs so as to heat them prior to the spraying operation. Mechanism is also illustrated for rotating the bulbs during the spraying operation, at which time a spray gun is moved so that the discharge nozzle thereof will enter the bulb for the spraying operation.

For the purpose of more clearly setting forth the present method, several "of the positions of the bulb and spray gun are illustrated in a diagrammatic-manner and a holder is shown by means of which the bulb may discharge, substantially in the form of a fan .15, as shown in Figures 2 and 3.

or cone, is produced by a discharge of air which enters a suitable conduit 13 and is directed across a tip 14 of the nozzle 11 by means of an angularly directed outlet orifice This discharge of air across the nozzle tip 14 results in the usual ejector effect to atomize and project finely divided material through a tubular passage in the conduit 13 A valve 16 may be provided for terminating the flow of coating material at will. In order to apply a coating to the bulb in accordance with the present method, the nozzle 11 is moved into the bulb at an angle to the longitudinal axis of the latter, as shown in Figures 1, 2 and 3. It is obvious, however, that the nozzle 11' may be moved through a predetermined path and the bulb may be held at an angle, in which case the spray nozzle may, for example, be moved horizontally. The result of this operation would, how'- ever, be the same as when moving the nozzle as setforth above.

According to the present method, the nozzle 11 is moved into the neck 17 of the bulb until adjacent to a point in a plane indicated by the dotted line 18, at which time the spray gun 12 may be operated by a manipulation of the valve 16 to project a fan or conical shaped discharge 19 of finely divided material. Thus the spray is produced within the article and the spray gun nozzle is then moved along the path indicated by the dotted line 20, which path has been chosen so as to keep the concentrated portion 21 of the spray as far from the surface or wall 22 receiving the spray as is possible, the distance of the nozzle with relation to the said wall being limited by the dimensions of the bulb.

As shown in Figure 4, an oven 23 is provided for heating the bulb prior to the spraying operation. The importance of elevating the temperature of the bulb prior to spraying will be appreciated, since it is evident that the spray must not run or flow when it is applied to the bulb but must be in such condition as to readily adhere to the surface and cover the same. The combination of the novel step of manipulating-the spray gun in relation to a heating surface is, therefore, an

important step in the present method.

As the gun moves into the bulb, the bulb is rotated at relatively high speed by means of any suitable mechanism, as a gear wheel 24 connected with a bulb holder 25 and in mesh with a gear wheel 26, the gear wheel 26 being rotated by any suitable source of power, not shown; A rotation of the bulb during the spraying operation causes an impingement of the pro ected coating material over the interior surface of the bulb. As soon as the 1 certain amount of spray material owing to the length of time to which the wall of the bulb is subjected to the spray discharge. It has been found that in order to obtain a uniform layer of spray material upon the inside surface of the bulb, the comparatively dense portion 29, which may be termed the main body of spray, should be moved so that this main body of spray does not reach the top portion 28 of the bulb.

The spray gun is, therefore moved until the main body of the spray is discharged adjacent to a point on the dead center of rotation of the bulb so that the free or roving particles of spray which are projected from the main body will be de osited on the upper wall of the bulb to produce a layer, which by reason of the relatively long time period during which the upper wall is exposed to the roving particles of the spray will produce a layer of material on the upper wall equal in density and thickness to the deposit upon the adjacent wall or the remainder of the in- 1 terior of the bulb. In producing a sprayed lamp bulb, the thickness of the coating may be determined by the character of the material used or by the duration of the spraying period, as, for example, the number of reciprocable movements or passes of the spray nozzle Within the bulb. If a light coating is to be obtained, it may only be necessary to move the spray nozzle into and out from the bulb, or if a heavier coating is desired, the spray nozzle may be moved back and forth several timeswithin the bulb.

It will be noted that the present method of coating involves the bodily mani ulation of a discharge of spray within the ody to be sprayed. This makes it possible to properly cover the wall of the ob ect such as a lamp which has asurface of undulatory form in longitudinal cross-section.

As illustrated in the drawing. the nozzle is shown as movable into and out from the bulb in such manner that the spray nozzle is held as far from the surface to be sprayed as practical. In practicing the present method, it has also been found that good results are obtained by moving the nozzle into the bulb through a path in accordance with the contour of the surface to be coated. By this manner of manipulating the nozzle, the outlet or discharge orifice of the nozzle may be maintained a uniform distance from the bulb.

As hereinbefore mentioned, .it has been been found that the degree of the density of the coating may be controlled by the number of movements or passes of the nozzle into and out from the bulb and that the rate of speed of rotation of the bulb may be varied so that the surface to be coated will be exposed to the spray for a longer or shorter period.

It has further been found that when utilizing the preheating step it is possible to dispense with a final baking step. The bulb when preheated-acts to dehydrate the applied coating and by leaving out the final baking step the operation of coating is expedited and a greater quantity of bulbs may be coated in a given time period than has heretofore been possible.

By producing) he spray after the nozzle has entered the bul it is possible to avoid a deposit of sprayed material upon the neck of the bulb. This is an advantage since after the bulb has been sprayed it is necessary to perform what is termed a sealing-in operation. This operation consists in fusing the neck of the bulb to another lamp part termed a mount, which latter part includes the filament and supporting structure. The sealingin operation necessitates the heating of the bulb neck until the same becomes plastic. If

a deposit of another material such as a coating is applied to the bulb neck, the operation of heating is more diflicult, since the coating absorbs heat and, therefore, makes it difficult to properly melt the glass and fuse the bulb neck to the lamp mount.

In the coating of lamp bulbs it has been found that satisfactory results are obtained by heating the bulb prior to the application of the coating to the bulb. In the apparatus shown and described herein, the same oven is used for preheating the bulb and for baking the same after the coating has been applied so that the baking temperature and the preheating temperature are the same, preferably about 350 C. It will be understood, however, that if desirable, two ovens may be employed and that the preheating temperature may be about 350 C. or above and the baking temperature may be about 350 'C. or

above.

Although any suitable coating composition may be employed, it has been found that the present method gives satisfactory results when a coating is provided containing sodium silicate, a filler'such as Kaolin and a pigment with a suitable amount of water mixed in a ball mill until a homogeneous mixture is obtained. A mixture of this character is well known in the lamp coating art and is more fully set forth in Patent 1,581,766.

Although a preferred embodiment of the invention is shown and described herein, it is to be understood that modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. The method of depositing a layer of a and effecting a movement of said spray into said body through a path intersecting the axis of rotation of the body. I

'2. The method of depositing a layer of a light difiusing material on the interior surface of a hollow body which comprises rotating the body about its longitudinal axis, moving a spray nozzle into the body creating a cone of sprayed material after the nozzle has moved within the body and moving said cone through a path intersecting the axis of rotation of the body.

3. The method of depositing a .layer of a light diffusing material on the interior surface of a substantially spherical hollow body which comprises rotating the body about its longitudinal axis, creating a cone of sprayed material within the body, moving said cone through a path intersecting. the axis of rotation of the body and causing the spray partijacent-to the neck portion thereof, moving the conical discharge through a path intersecting the axis of rotation of the bulb and causing particles of discharged material to travel in a direction substantially perpendicular to the bulb wall.

5. The method of depositing a uniform layer of a light diffusing material on the interior surface of a lamp bulb which comprises, creating a conical discharge. of coat ing material within the bulb at a point adjacent to the neck portion thereof reciprocating the conical discharge through a path intersecting the axis of rotation of the bulb so as to sweep the interior surface thereof with sprayed material and terminating the spray discharge.

6. The method of depositing a layer of light diffusing material on the interior surface of a lamp bulb which comprises, heating the bulb to produce a moisture absorbing atmosphere therein, creatin a discharge of an aqueous solution of coating material and moving the discharged material into the bulb with the source of discharge an appreciable distance from the bulb wallso that discharged particles will take a relatively long path through. the moisture absorbing atmosphere and produce a non-flowing uniform layer upon the bulb wall.

7. The method of depositing a layer of light diffusing material on the interior sur- I face of a lamp bulb which comprises creating phere. within the body, producing a spray of an aqueous solution of finely dividedcoating material, rotatingthe body about its longitudinal axis, moving the said spray through a path intersecting the axis of rotation of said body and causing the sprayed particles to travel in a direction substantially'transverse to the surface of said body.

9. The method of depositing a layer of light diffusing material on the interior surface of a substantially spherical hollow body which comprises creating a heated atmosphere within the body, producing within the body a spray discharge of an aqueous solution of a coating material, rotating the body about its longitudinal axis, moving the spray discharge through a path intersecting the axis of rotation of the body, causing the discharged sprayed particles to travel in a path at substantially right angles to the surface of said body and terminating the spray discharge within the body.

In testimony whereof, we have hereunto subscribed our names this 23rd day of July,

AARON M. HAGEMAN. ALBERT F. LINDSTROM. 

